Micronutrients are also called trace elements because only a very small amount — a trace of each is required for healthy growth. They include iron, boiftn, manganese, copper, zinc, and molybdenum.
The importance of these nutrients has become more obvious with increased use of synthetic fertilizers. When farmers and gardeners had to depend on manures for major nutrients, they didn't have to worry about micronutrients. The current generat ion of synthetic fertilizers is so purified that few if any micronutrients remain in them. As a result, deficiency symptoms (once thought to be diseases) are now more common. Crops grown on soils lacking these nutrients may fail to supply human dietary needs, even if plants don't appear to suffer.
You may never have to worry about micronutrients if you routinely add compost or manure, or if you use fish emulsion and/or liquid seaweed as fertilizers from time to time. Micronutrients should never be added unless soils are known to be deficient, and then only in the recommended amounts. The difference between helpful and harmful amounts is incredibly small. Also, deficiencies of micronutrients are often irregular, occurring only in some areas of a garden. Pockets of poor drainage, where soil pH differs from t he surroundings, or where soil has washed away are likely spots for small-scale deficiencies.
Chlorine, Nickel, and Cobalt
Like carbon, oxygen, and hydrogen, chlorine and nickel don't need to be applied to soils. Researchers have proved that plants can't grow without them, but gardeners don't need to worry about them.
Cobalt is required by some plants and many microorganisms, including nitrogen-fixing bacteria. The amount of cobalt needed is too small even to measure; so again, don't worry about it.
The element silicon doesn't qualify as essential because many plants grow well without it. But some plants benefit from added silicon, so think of it as a beneficial rather than an essential nutrient. Corn contains high levels of silicon, which helps make cornstalks stiff. As you might expect, corn is one of the plants that benefits from added silicon. Silicon also appears to increase disease resistance. Sand (silica) is naturally rich in silicon. Greensand (a special type of sand that's green in color) is best for adding silicon to soil; it s also a good source of potassium. Granite dust is anotiier good source. Both of these are also excellent slow-release sources of essential micronutrients.
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How Small Is a Tract?
To give you an idea of the difference between major and traee nutrients. consider the needs of corn. During the growing season, an acre of corn can easily withdraw \M pounds (68,(XX) g) of nitrogen from the soil. Hut those same plants might withdraw only half an ounce (15 g) of the trace element boron from an acre. That means corn needs over 4,500 times as much nitrogen as boron in its diet!
A deficiency of an essential nutrient harms plants by slowing or stopping particular functions. In order to grow, plants have to produce new cells If a nutrient required for cell division is lacking, the plant can t make enough new cells, so growth slows dramatically or even stops.
By the time nutrient deficiencies become visible, some damage has already been done. A soil test can detect deficiencies before they cause damage. However, since soil changes over time, and since you can't test the soil in every part of your garden, it helps to know how to recognize common nutrient deficiencies. These are easiest to recognize when they're severe and hardest to recognize when more than one is present at one time. Consult the chart on pages 204-205 to help match your plant's symptoms to a probable cause. Try to figure out the cause of any nutrient imbalance before you attempt to correct it. If the "deficiency" is caused by a physical soil problem (see box at right) or interference from too much of another nutrient (which will show up in a soil test), you won't fix anything by dumping on fertilizer. Once you identify a specific deficiency, turn to chapter 6 for information about the best sources of that nutrient.
Is It Really a Deficiency?
Before you assume you're missing nutrients, rule out other causes. Addressing such causes can alleviate deficiency symptoms with no added fertilizer. Using a foliar spray of a liquid seaweed/fish emulsion combination will keep plants growing until long-term improvements occur.
Plants' ability to absorb existing nutrients. Aphids and spider mites cause yellowed leaves. Viral diseases can cause mottled, yellow or deformed leaves.
AlSf o,aLSOil P™ble",s- f nutrient may be present but locked UP by P°°r aeration or poor drainage. ?
a aMi* ZZi t " 2f 7'* C°mm0n CaUS£ °f lodd*S nutrients. To maximize nutrient availability, ti y to maintain a pH of 6.3 to 6.8. ^^
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Disease or Deficiency?
Whiptaili which is recognized by weirdly distorted, long leaves of cabbage and related plants, is also caused by molybdenum deficiency.
Symptoms on upper leaves? Some nutrients stay put; they can't move within the plant because they're built into the cell structure. Sulfur, calcium, iron, manganese, boron, and copper are needed to make healthy new leaves, but plants can't borrow them from elsewhere if there's not enough. As a result, deficiency symptoms of these structural elements show up first on young, upper or outer leaves.
Symptoms on lower leaves? Some nutrients get around — they're easily shuttled around within the plant: nitrogen, phosphorus, potassium, magnesium, molybdenum, and zinc. That means if plants aren't getting enough, they can move these to young, growing tissue, where they're needed most. As a result, deficiency symptoms of these mobile elements show up first on older, lower leaves, eventually spreading to the rest of the plant.
CREATING FIRTiLI SOIL
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